1. Field of the Invention
The present invention pertains, in general, to a light emitting diode (LED) and, in particular, to a GaN light emitting diode for a flip-chip bonding, which secures a sufficient bonding area while optimizing an electrode arrangement, prevents an electric current from concentrating on a predetermined portion, and has higher brightness and reliability, and a method of fabricating the same.
2. Description of the Related Art
Acting as a semiconductor device emitting light by the recombination of electrons with holes, a light emitting diode (LED) is widely used as a light source in light communication devices and electronic devices.
A frequency of light emitted from the light emitting diode is utilized as a band-gap function of a material used in the semiconductor device. A wavelength of the light, in place of the frequency, may be used as the band-gap function. In the case of using the semiconductor material with a small band gap, the light emitting diode emits photons with low energy and long wavelengths. On the other hand, in the case of using the semiconductor material with a wide band gap, the light emitting diode emits photons with short wavelengths.
For example, when AlGaInP is used as a material in a semiconductor device, the light emitting diode emits light with red wavelength, and when a SiC or III group nitride (particularly, GaN) semiconductor device is used, the light emitting diode emits light with blue or violet wavelengths.
Of the various semiconductor materials, a Ga-based light emitting diode does not form a bulk single crystal of GaN, thus a substrate proper to grow the GaN crystal must be used and a representative material of the substrate is sapphire (i.e. aluminum oxide (Al2O3)).
FIG. 1 is a sectional view of a conventional GaN light emitting diode. The GaN light emitting diode 10 includes a sapphire substrate 11, a GaN light emitting structure 13 formed on the sapphire substrate 11, and a p-electrode 15 and an n-electrode 16 formed on the GaN light emitting structure 13.
The GaN light emitting structure 13 includes a n-type GaN clad layer 13a, an activation layer with a multi-quantum well structure 13b, and a p-type GaN clad layer 13c, which are sequentially formed on the sapphire substrate 11. In this regard, the GaN light emitting structure 13 is formed according to a metal organic chemical vapor deposition (MOCVD) process. At this time, a buffer layer (not shown) including an AlN/GaN may be formed so as to improve the lattice matching of the GaN light emitting structure 13 with the sapphire substrate 11 before the n-type GaN clad layer 13a of the GaN light emitting structure 13 is built.
Additionally, the p-type GaN clad layer 13c and the activation layer 13b of the GaN light emitting structure 13 are dry-etched to expose a portion of the n-type GaN clad layer 13a. 
The n-electrode 16 and p-electrode 15 are respectively formed on the exposed portion of the n-type GaN clad layer 13a and a portion of the p-type GaN clad layer 13c which is not etched, so that a predetermined voltage is applied through the p- and n-electrodes 15, 16. In this regard, a transparent electrode 14 may be formed on the p-type GaN clad layer 13c before the p-electrode 15 is formed on the p-type GaN clad layer 13c so as to increase a current implant area and so as to prevent deterioration of the brightness of the light emitted from the light emitting diode.
The GaN light emitting diode may be formed in a package in accordance with a die bonding process using a chip side up manner. At this time, the light emitting diode must emit light in a direction toward which the p-electrode 15 and n-electrode 16 are formed, but the light emitting diode does not emit the light at a portion in which the two electrodes 15, 16 are formed. Additionally, heat is discharged from the light emitting diode at a slow speed when the light emitting diode emits the light because of the low thermal conductivity of sapphire constituting the substrate, thus the life span of the light emitting diode is reduced.
To avoid the above disadvantages, many studies on a light emitting diode for a flip-chip have been conducted, in which the light emitting diode 10 of FIG. 1 is upset to mount the p-electrode 15 and n-electrode 16 on a printed circuit board or a lead frame according to a die-bonding process, thereby accomplishing a flip-chip bonding. At this time, the light emitting diode emits light through the sapphire substrate 11.
FIG. 2A is a plan view illustrating a conventional light emitting diode with a flip-chip structure and FIG. 2B is a sectional view taken along the line A—A of FIG. 2A, and FIGS. 2A and 2B are shown in U.S. Pat. No. 6,333,522 (title: Light-emitting element, semiconductor light-emitting device, and manufacturing methods therefor, Registration date: Dec. 25, 2001).
As described above, a light emitting diode 20 includes a buffer layer 22, an n-type GaN clad layer 23a, an activation layer 23b, and a p-type GaN clad layer 23c sequentially formed on a sapphire substrate, and the activation layer 23b and p-type GaN clad layer 23c are dry-etched. After a portion of the n-type GaN clad layer 23a is exposed, an n-electrode 26 is formed on the exposed portion of the n-type GaN clad layer 23a, and a p-electrode 25 is formed on a portion of the p-type GaN clad layer 23c which is not etched. Additionally, a transparent electrode 24 is layered between the p-type GaN clad layer 23c and p-electrode 25.
Subsequently, microbumps 27, 28 made of Au or an Au alloy are formed on the p-electrode 25 and the n-electrode 26, respectively.
The light emitting diode 20 of FIG. 2 is mounted on a lead frame of an LED device by bonding the microbumps 27, 28 of the light emitting diode to the lead frame.
However, the light emitting diode of U.S. Pat. No. 6,333,522 is disadvantageous in that the life span of the light emitting diode is reduced because an optimum, uniform electrical current is not obtained through the light emitting diode and the electrical current applied to the light emitting diode during the operation of the light emitting diode is concentrated into a predetermined portion of the device even though the light emitting diode is integrated with a Si diode element and a substrate to reduce an electrical connection area and increase the brightness and light emitting efficiency.